Fig. 1: Scheme and structure of xylene isomers and ZU-61.

a Electron density (e/au3) of each xylene isomers. b Schematic illustration of the porous adsorbent with “Lewis basic-binding sites and rotational flexibility”. c Structure of ZU-61 with rotational ligand of NbOF52− anion and bipyridine (d). e Thermogravimetric analysis results of ZU-61, SIFSIX-1-Cu, and ZU-61-Cu.